Electrical switching device



E. B. KING 44,179

ELECTRICAL SWITCHING DEVICE Filed June 28, 1943 8 InveJor I B v fiytiiajli fim Attorney Patented July 16, 1946 UNITED STATES PATENT OFFICEApplication June 28, 1943, Serial No. 492,616 In Great Britain April 17,1942 4 Claims. 1

This invention relates to electrical switching arrangements and has asits main object the production of a, switching arrangement, for example,for controlling a relay device, which is responsive to changes invelocity of apparatus carrying the arrangement.

The improved switching arrangement, according to the invention,comprises an acceleration switch arranged to operate its contacts due tothe inertia of a moving part during acceleration in a predetermineddirection and a deceleration switch arranged to operate its contacts dueto the inertia of a moving part during deceleration, one of the switchesbeing irreversible, that is. remaining closed (or open) after operation,so that both switches are in their operated positions after anacceleration period followed by a deceleration peried, or vice versa.

Preferably the irreversible switch consists of a switch of the typeemploying a conducting liquid, such as mercury, and including a.capillary tube substantially parallel to the direction of motion alongwhich the liquid is forced to close contacts at the remote end of thetube when the rate of change of velocity (the acceleration or thedeceleration) exceeds a predetermined value for a predetermined time.Conveniently one or more intermediate traps or bulbs are providedbetween the ends of the capillary tube to prevent closing of the switchdue to accidental shocks or to vibration.

The switch which is not irreversible may comprise a tubularnon-capillary switch employing a conducting liquid, such as mercury, andarranged substantially parallel to the direction of motion with thecontacts to be closed at the app end of the tube.

The capillary switch may be so arranged and dimensioned that it closeswhen the force is a large multiple of the force required to close thenon-capillary switch, or the switches may be so dimensioned and theconducting liquids so chosen that the forces which cause closing of therespective switches may be of substantially the same order of magnitude.

In a convenient practical arrangement a capillary acceleration switchand a non-capillary deceleration switch have their contacts connected inseries in a circuit of a relay, for example, in the anode circuit of agas-filled triode relay, whereby the circuit is prepared by closing ofthe capillary switch during acceleration and completed by closing of thenon-capillary switch when deceleration begins.

Such a switching arrangement may be combined with a relay for initiatingdetonation of the charge of a rocket or other non-rotated projectile, inwhich case the switches are so constructed and supported as to withstandthe stresses due to the high acceleration of the projectile. Anotherapplication of such arrangement is in combination with a relay forcontrolling elevators and/or steering mechanism of an aircraft, therelay being energised to efiect a control operation when the aircraftdecelerates following a high speed evolution; for example, a steep dive.Such an arrangement can also be used for con trolling the detonation ofa projectile or bomb when it reaches a predetermined depth below thesurface of the water, the acceleration switch being operated during aninitial acceleration period whilst the deceleration switch operates whenthe projectile slows up immediately following its immersion in thewater.

A construction of the switch arrangement according to the inventionwhich is particularly suitable for controlling the arming of a proximityfuze for rockets or other non-rotating projectiles will now be describedby way of example with reference to the accompanying drawing in whichFig. 1 shows a preferred form of capillary switch;

Fig. 2 shows a preferred form of non-capillary switch; and

Fig, 3 shows the method of assembling the switches.

The function of a switching arrangement, ac cording to the invention, ina proximity fuze is mainly as a two-stage arming device to ensure thatthe projectile is safe to handle before it is fired, that electricalapparatus, such as thermionic valves, forming part of the fuze isprepared for operation during the preliminary part of the flight of theproectile without the fuze being completely armed whilst it is close toand therefore sensitive to the ground, and, finally, that completearming is efiected when the projectile is at a sufiicient distance fromthe ground to b substantially immune from ground eiiects.

In such fuzes, detonation is controlled by a relay which preferablycomprises a gas-filled ionic valve, such, for example, as a valve soldunder the registered trade-mark Thyratrcn, having a control grid bymeans of which the relay is triggered. The triggering impulse may besupplied, preferably through an amplifier, from a photoelectric cellarrangement responsive to changes in illumination caused by the targetor by a radio receiver responsive to radio-frequency os- 3 cillationsreflected from the target or transmitted from the ground.

The switching arrangement according to the invention is so arranged thatthe acceleration switch A, which is the irreversible switch, when itoperates completes the filament and anode circuits of any thermionicvalves employed in the amplifier and other apparatus and also closes apoint in the anode circuit of the gas-filled relay. The circuits arethus prepared for operation during the initial acceleration of theprojectile.

Complete arming of the fuze during this period is prevented by the opencontacts of the deceleration switch B, these contacts being included inthe anode circuit of the gas-filled relay. Thus, when the projectilebegins to deceler-ate, that is, when, in the case of a rocket, thepropelling charge is fully burnt, the deceleration switch B closes andthe fuze is then fully armed so that it responds to the reflectedradiations from the target as soon as the projectile approaches sufficiently close thereto.

In such an arrangement a separat acceleration switch is provided foreach of the independent circuits to be closed, each switch convenient--1y consisting of a glass capillary tube having an internal bore A!(Fig. 1) of between 0.12 and 0.16 millimetre in diameter. The tube,which is about centimetres overall length, has at its lower end, that isthe end nearest to the rear end of the projectile, a small bulb A2 ofbetween 3 and 4 millimetres in diameter through the wall of which aresealed two metal Wires A3 of a suitable alloy to form a vacuum-tightseal with the glass, the inner ends of these wires, which project intothe bulb, being spaced apart from one another. At the upper end of thetube there is another bulb A4 containing a small amount of mercury. Thetube is evacuated to a low pressure and sealed at its upper end. Theamount of mercury and the bor of the capillary are such that, due tosurface tension, the mercury will not enter the capillary as a result ofaccidental shocks or normal vibration, but, when the switch is subjectedto high acceleration, for example an acceleration of the order of 40 g.,the thrust due to the inertia of the mercury is sufiicient to forcemercury along the bore of the tube. If such acceleration is maintainedfor a suflicient time, which depends on the length of the tube, themercury will fill the bulb at the lower end of the tube and thuscomplete a low resistance contact between the wires projecting into thebulb. The switch thus closed will remain closed unless it is subjectedto a correspondingly high acceleration in the opposite direction.

In order to ensure that vibration will not cause mercury to reach thelower bulb, an intermediate trap or bulb A5 may be formed in thecapillary about midway between the ends.

If mercury should penetrate to such trap due to vibration, it is likelyto return to the upper bulb as a result of further vibration.

A preferred construction of deceleration switch is shown in Fig. 2 andcomprises a glass tube having a length of approximately 4 centimetresand an internal diameter of between 4 and 5 millimetres. In this case,contact wires Bl B2 project into the upper end of the tube which ispreferably of slightly reduced internal diameter, the inner ends of thecontact wires preferably project ing beyond the point at which thediameter of the tube is reduced, for example, from the upper end of thetube to a. distance of between a. half and a third of the length of thetube. The

tube contains suflicient mercury B3 to produce adequate low-resistancecontact between the two wires when the tube is inverted, but the'amountof mercury should not be such as to prevent free movement thereof in thewider portion of the tube. A small quantity of a. suitable powder suchas aluminium oxide, may be added to the mercury to facilitate freemovement thereof. The tube may be exhausted or may be filled with air orother gas at a suitable pressure.

The dimensions of the acceleration and deceleration switches describedabove are such that the acceleration switch will be operated by anacceleration of the order of 40 times that of gravity averaged over aperiod of from 0.4 to 1 second, whilst the deceleration switch issensitive to a deceleration force of approximately 0.3 times that ofgravity for a very short period.

The several switches are mounted with their axes parallel to one anotherand to the axis of the projectile, as shown in Fig. 3. In order thatthey will withstand the high stresses due to the rapid acceleration ofthe projectile, they are assembled and bound together in a suitableplastic or semi-plastic material such as paraflin-wax. Alternatively,they can be mounted in grooves in a former of ebonite or other syntheticinsulating material, and enclosed in a varnished paper tube, thecomplete assembly being, if desired, impregnated with a suitable bondingmaterial.

It is to be understood that the specific construction of switchingarrangement described above is by way of example only and that thedimensions and the mounting of the individual switch elements can bevaried as desired to suit the use of the switching arrangement. It willalso be appreciated that whilst various applications of an arrangementaccording to the invention have been specifically referred to, such anarrangement can be used in any apparatus or vehicle where it is desiredto complete (or to open) an electric circuit as a result of successiveacceleration-decal eration periods or vice versa. When the circuit is tobe opened the capillary switch or switches will, of course, be arrangedso that normally the conducting liquid closes the contacts but movesunder the influence of the appropriate acceleration or deceleration toan empty bulb at the remote end of the capillary.

I claim as my invention:

1. In a body subject to changes of velocity, an electrical switchingarrangement for controlling electrical circuits carried by the bodycomprising a first switch adapted to operate in response t a change invelocity of one sign and thereafter to remain locked in the operativeposition and a second switch adapted to operate in response to a changein velocity of the opposite sign said first switch comprising acapillary tube for each pair of contacts to be operated, a bulb at eachend of said capillary, a pair of said cont-acts protruding through thewall into one bulb and a conducting fluid in one bulb, and said secondswitch comprises a non-capillary tube for each pair of contacts to beoperated, a pair of said contacts protruding through the wall into oneend thereof and a conducting fluid at one end thereof.

2. In a body subject to changes of velocity an electrical switchingarrangement for closing in two stages electrical circuits carried by thebody comprising for each pair of contacts to be closed in the firststage a capillary tube, a bulb at one end of said tube, a pair of saidcontacts in the bulb and a mercury reservoir at the other end of saidtube, said mercury flowing through said tube into the bulb in responseto a change of velocity of one sign to bridge said pair of contacts andto complete the first stage of closure of said circuits, and for eachpair of contacts to be closed in said second stage a non-capillary tube,a pair of said contacts protruding into one end of the bore of the tube,a globule of mercury adapted to move freely in the bore in response to achange of velocity of the opposite sign to bridge the contacts and tocomplete the second stage of closure of said circuits.

3. An electrical switching arrangement according to claim 2 wherein eachcapillary tube iS provided with an intermediate bulb substantiallymidway between its ends, said intermediate bulb acting as a trap toprevent mercury reaching the contacts as a result of vibration.

4. In a body subject to changes of velocity, an

electrical switching arrangement for controlling electrical circuitscarried by the body comprising.

a first switch adapted to operate in response to a change of velocity ofone sign and thereafter to remain locked in the operative position, anda second switch adapted to operate in response to a change in velocityof the opposite sign, said first switch including a pair of contacts tobe operated, a mass of material arranged to move freely in one directionfrom one position to another and to close said contacts in one of saidpositions and means for preventing the return of the mass in theopposite direction, and said second switch includes non-capillary tube,a pair of contacts to be operated protruding through the Wall into oneend thereof, and a conducting fluid at one end thereof.

EDWARD BOLTON IHNG.

